QCD and the η′ mass:: Instantons or confinement? -: art. no. 074502

We argue that lattice calculations of the eta(') mass in QCD with N-c=2 colors performed at a nonzero baryon chemical potential can be used to study the mechanism responsible for the mass of the eta('). QCD with two colors is an ideal laboratory because it exhibits confinement, chiral symmetry breaking and a would-be U(1)(A) Goldstone boson at all densities. Since the instanton density and the confinement scale vary with density in a very different way, instantons are clearly distinguishable from other possible mechanisms. There is an instanton prediction for the eta(') mass at large density that can be compared to lattice results. The density dependence of the instanton contribution is a simple consequence of the integer topological charge carried by the instanton. We also argue that N-c=3 color QCD at finite isospin density can be used in order to study the origin of OZI violation in the scalar sector.